1. Field of the Invention:
This invention relates to impact modification of linear, saturated thermoplastic poly(C.sub.2 to C.sub.8 alkylene terephthalates).
2. Description of the Prior Art:
Poly(C.sub.2 to C.sub.8 alkylene terephthalates) are limited in their use as thermoplastic molding resins due to their relatively low notched impact strength.
Various modifier systems for improving the toughness have been suggested. Farnham and Goldman in U.S. Pat. No. 4,096,202 of June 20, 1978 have suggested an impact modification system comprised of a multiphase composite interpolymer having a first phase polymerized from a monomer system comprised of about 75-99% C.sub.1 to C.sub.6 alkyl acrylate, 0.1-5% crosslinking monomer, and 0.1-5% graftlinking monomer, and about 75 to 5 percent of a final, rigid, thermoplastic phase. Nakamura et al, U.S. Pat. No. 3,864,428, disclosed blends of aromatic polyester, aromatic polycarbonate, and butadiene-based, core-shell polymers wherein the polycarbonate constituted 10-75% and preferably 20-60% of the tertiary mixture. Shell and Fromuth in U.S. Pat. No. 4,180,494 of Dec. 25, 1979 disclose high impact compositions comprising about (a) 25-95% aromatic polyester, (b) about 1-8% of an aromatic polycarbonate, and (c) the balance to make 100% of a core-shell polymer having a butadiene-based core.
In the teachings of Nakamura et al and of Fromuth and Shell, only butadiene-based, core-shell impact modifiers are disclosed. Butadiene-based polymers suffer from inherent thermal instablity, which is well known to those skilled in the art, and thereby are excluded from most long-term, high temperature applications. Furthermore, polybutadiene polymers have a glass transition temperature, T.sub.g, of about -80.degree. C. Acrylate-based polymers, on the other hand, such as those disclosed in this invention, have T.sub.g 's of about .ltoreq.-40.degree. C. It is not obvious that an impact modifier with a significantly higher T.sub.g, such as those disclosed in this invention, would function well or as efficiently as those based on a butadiene polymer.